(1) Field of the Invention
The present invention relates to an aminocarboxylic acid chelating agent excellent in biodegradability and to the uses of the chelating agent. More particularly, it relates to a biodegradable chelating agent in the form of solid, aqueous solution or slurry excellent in handleability and a detergent composition having excellent detergency and high in biodegradability which comprises the biodegradable chelating agent.
(2) Description of the Related Art
In general, chelating agents used in the form of solid are stored in the form of powder or flake in a bag or a hopper. Solid chelating agents gradually change to a hard mass due to the hardening property depending on accumulation condition and period and preservation condition and period. Therefore, the mass must be crushed just before the use and this is very inconvenient in handling.
Chelating agents used as aqueous solution or slurry are not needed to crush, but have serious problems such as deterioration in purity owing to decomposition in aqueous solution and coloration.
Generally, aminocarboxylic acid chelating agents are widely used as components of photographic bleaching agents, detergent compositions, detergent builders, heavy metal sequestering agents, stabilizers for peroxides and the like.
The detergent compositions are widely used for household cleaning of kitchenware, household cleaning of clothing, cleaning of dinnerware for business purpose, cleaning of plant, cleaning of clothing for business purpose, and the like. Furthermore, they are used as bleaching agents, descaling agents, metal sequestering agents, and the like together with additives suitable for the use.
Sodium tripolyphosphate which has hitherto been used as detergent builders is high in chelating performance. However, it contains phosphorus and causes eutrophication of rivers and lakes when it is discharged into environment. Thus, it is no longer used at present.
Zeolites which are used as detergent builders at present have disadvantages that they are low in chelating performance and have no biodegradability because they are inorganic materials. Furthermore, zeolites are insoluble in water and have a restriction in that they cannot be used for liquid detergents, especially clear liquid detergents. Moreover, zeolites have many problems such that they stick to inner wall of drainage pipes or settle at the bottom of rivers to cause formation of sludges. Therefore, the attempt is being made to reduce the amount of zeolites used and substitutes for zeolites which have sufficient chelating power and detergency have been desired, but such substitutes have not yet been obtained.
Of the aminocarboxylic acids which have been used as detergent builders, ethylenediaminetetraacetic acid (EDTA) has an excellent chelating power in a wide pH range, but is poor in biodegradability and is difficult to degrade by the usual waste water treatments which employ activated sludges. Furthermore, nitrilotriacetic acid (NTA) has a certain biodegradability, but is not preferred from the point of environmental health because it has been reported that NTA has teratogenicity and nitrilotriacetic acid-iron complex has carcinogenicity. Among other conventional aminocarboxylic acids, those which are excellent in chelating performance, but are low in biodegradability have the difficulty that they accumulate as injurious heavy metals in the environment when they are discharged into the environment. Various compounds have been studied as for the above-mentioned organic amino acids, but those which are excellent in chelating performance and biodegradability have not yet been reported at present.